An example of an obstacle detection system related to the present invention is described in reference 1 (Japanese Patent Laid-Open No. 2001-187553). FIG. 25 is a block diagram showing an example of the arrangement of an obstacle detection system related to the present invention. As shown in FIG. 25, the obstacle detection system described in reference 1 includes a vehicle 10, display (not shown), camera 20, image processing apparatus 30, steering angle sensor 40, wheel speed sensor 60, and pulse counter 50.
The obstacle detection system shown in FIG. 25 operates in the following way. During movement of the vehicle 10, the camera 20 time-serially senses the vicinity of the vehicle. At the same time, the steering angle sensor 40, wheel speed sensor 60, and pulse counter 50 measure vehicle moving data. Projective transformation to a second viewpoint is performed to obtain an image which satisfies a condition that all sensing targets contained in an image sensed at a first viewpoint exist on a plane. A difference image between the thus obtained image and an image actually sensed at the second viewpoint is generated. The generated difference image is used for obstacle detection.
The obstacle detection system shown in FIG. 25 acquires vehicle moving data from the steering angle sensor 40, wheel speed sensor 60, and pulse counter 50. Reference 2 (Gideon P. Stain, Ofer Mano, and Amnon Shashua, “Proceedings of the IEEE Intelligent Vehicle Symposium 2000”, pp. 362-368, Oct. 3, 2000, USA) describes another method of acquiring vehicle moving data. The vehicle moving data acquisition method described in reference 2 will be explained.
Initial vehicle moving data is acquired, including a moving amount in the vehicle traveling direction, a rotation amount about a horizontal axis perpendicular to the vehicle traveling direction, and a rotation amount about a vertical axis. These data are acquired by time-series image sensing by a camera mounted on a vehicle and measurement using a speed meter or calculation at the preceding viewpoints.
Projective transformation to a second viewpoint is performed based on the vehicle moving data to satisfy a condition that all sensing targets contained in an image sensed at a first viewpoint exist on a plane. Based on the difference image between the thus obtained image and an image actually sensed at the second viewpoint, the probability density of actual moving data is calculated. Moving data including a moving amount in the vehicle traveling direction, a rotation amount about the horizontal axis perpendicular to the vehicle traveling direction, and a rotation amount about the vertical axis, which ensure the maximum probability, is calculated.